1. Field of the Invention
The present invention relates to a method for manufacturing a wafer level chip stack package.
2. Description of the Related Art
The electronic industry is continually seeking methods, techniques and designs that will result in the manufacture of electronic products that are smaller, lighter, faster, more efficient, operate at higher speeds, provide multiple functions and/or result in improved performance, at an effective cost. One of the methods that has been used for attaining such goals is improved package assembly techniques that have resulted in the development of new types of packages such as chip scale or chip size packages (CSP). The CSPs may be manufactured at chip level or at wafer level, with those manufactured at the wafer level also referred to as wafer level chip scale packages (WLCSP).
Typically, a WLCSP will include a stack of a plurality of semiconductor chips that are interconnected by bump connections. For example, each semiconductor chip may include electrode pads formed on the active surface and through electrodes formed at or along the edges of the semiconductor chip. The through electrodes may, in turn, be connected to the electrode pads by redistribution lines. The corresponding through electrodes provided on adjacent semiconductor chips may then be electrically connected with bump connections. Although the semiconductor chips in the chip stack are physically and electrically connected, the formation of such a stack using only bump bonding tends to result in a space or void being formed between the opposing surfaces of two adjacent semiconductor chips. Such spaces may cause reduced mechanical strength and increase the likelihood of reliability faults in the chip stack package. Therefore, the space between adjacent semiconductor chips should be filled to produce a stronger, more durable chip stack package. In a conventional method for manufacturing a WLCSP, liquid adhesive and/or adhesive tape may be used to fill the space between adjacent semiconductor chips.
FIG. 1 is a cross-sectional view of an example of a conventional WLCSP 130. The WLCSP 130 illustrated in FIG. 1 may be manufactured by sequentially using wafer preparing, wafer stacking, wafer sawing and liquid adhesive injection processes.
A plurality of substantially identical wafers (not shown), each having a plurality of semiconductor chips 111, may be prepared using any conventional semiconductor manufacturing process. Each semiconductor chip 111 is provided with a plurality of through electrodes 113 arranged in a peripheral region of the semiconductor chip and bumps 117 formed on at least one end surface of the through electrodes. Alternatively, instead of forming the bumps 117, the through electrodes 113 may be constructed so as to protrude above a surrounding surface of the semiconductor chip 111 for providing connection between adjacent semiconductor devices.
A plurality of such wafers are then vertically stacked so that the corresponding through electrodes 113 and/or bumps 117 of adjacent semiconductor chips 111 are aligned and brought into contact so as to provide electrical connection between adjacent semiconductor chips. The stacked wafers are then divided into individual chip stack packages 130 and a liquid adhesive 123 may be injected into a space remaining between adjacent semiconductor chips 111 and cured to reduce or eliminate voids from the chip stack package.
The WLCSP in which the spaces between adjacent semiconductor chips has been filled with an adhesive may exhibit improved mechanical strength and reliability in comparison with a similarly constructed WLCSP in which the vacant spaces between the adjacent semiconductor chips have not been filled.
However, because the liquid adhesive 123 used to fill the spaces between the adjacent semiconductor chips 111 typically includes metallic and/or non-metallic particulate filler materials, its flow characteristics may make it difficult to fill the space(s) between adjacent semiconductor chips completely or consistently, particularly for chip stacks having relatively small chip-to-chip spacing. Thus, as illustrated in FIG. 1, a WLCSP 130 manufactured with such a liquid adhesive 123 may still include one or more vacant spaces or voids 135 between adjacent semiconductor chips 111. One proposal for addressing the problem of voids in a WLCSP is to use an adhesive tape rather than a liquid adhesive.
FIG. 2 is a cross-sectional view of another example of a conventional WLCSP 230. The WLCSP 230 illustrated in FIG. 2 may be manufactured by sequentially using wafer preparing, adhesive tape attaching, wafer stacking and wafer sawing processes.
A plurality of substantially identical wafers (not shown), each having a plurality of semiconductor chips 211, each having a plurality of semiconductor chips 111, may be prepared using any conventional semiconductor manufacturing process. Each semiconductor chip 211 will typically include a plurality of through electrodes 213 arranged in a peripheral region of the semiconductor chip. The through electrodes 213 may be constructed with protruding portions (not shown) that extend above the adjacent surface of the semiconductor chip or may be provided with bumps 217 formed on at least on surface of the through electrodes.
An adhesive tape 221 may then be attached to the semiconductor chip 211 while still at the wafer level, the adhesive tape 221 typically having openings provided therein to avoid interfering with the bumps 217 or protruding portions (not shown) by maintaining some minimum separation distance between the adhesive tape and the connecting structures.
A plurality of such wafers are then vertically stacked so that the corresponding through electrodes 213 and bumps 217 of adjacent semiconductor chips 211 are aligned and brought into contact so as to provide electrical connection between adjacent semiconductor chips. The stacked and connected wafers may then be divided into individual chip stack packages 230.
A WLCSP manufactured using an adhesive tape may exhibit improved filling performance and mechanical strength in comparison with a WLCSP manufactured with a liquid adhesive. However, the adhesive tape may result in uneven pressure being applied to one or more of the semiconductor chips during a chip stacking process that may result in warpage of one or more of the semiconductor chips. Further, as illustrated in FIG. 2, during the assembly process, the temperature and/or pressures applied to the chip stack may be sufficient to cause the adhesive tape composition 224 to liquefy and flow out from between the adjacent semiconductor chips and onto the lateral or side surface(s) of the package.